Table ii



United States Patent "ice 3,127,265 Ni-Cr-Co ALLDYS Howard S. Avery, Mahwah, N.J., assignor to American Brake Shoe Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Aug. 8, 1951, Ser. No. 130,000 3 Claims. (Cl. 75-171) This invention relates to heat and corrosion resistant alloys for structural parts in industrial furnaces and like installations where structural parts must possess high resistance to oxidation in addition to exceptional levels of hot strength, and which can be cast or forged. This application is a continuation-in-part of application Serial No. 808,024, filed April 22, 1959, now abandoned.

For engineering applications involving elevated temperature service, the so-called creep characteristics of the alloy used for structural materials are frequently of major importance as well as oxidation and corrosion resistance characteristics. Thus, in such applications failure of structural parts can result from excessive creep (plastic deformation) as Well as rupture under load due to external or internal deterioration caused by oxidation and corrosion occurring progressively inwardly of the part, as in the presence of hot corrosive flue gases. Engineering developments in the petro-chemical industry, in the manufacture of furnace equipment and in other high temperature industries are limited by the capabilities of available alloys. For example, there is need for oxidationresistant alloys with high creep and rupture strengths in the temperature range of 1800 F. to 2300 F. For the cast industrial heat-resistant alloys (such as the Alloy Casting Institute grades) a few display reasonably good oxidation resistance up to 2150 F., but their strength is low. Some exceptional properties are reported with cobalt-base alloys having 55 percent or more cobalt, but these are expensive. In comparison, the cobalt content in the alloys of the present invention need not exceed 3,127,265 Patented Mar. 31, 1964 iron. It has heretofore been proposed to use as an addition one or more of molybdenum, titanium With aluminum, and columbiurn for enhancing the hot strength of such alloys. For one reason or another, these additions have rather serious drawbacks and therefore limit utilization of the resultant alloy. The titanium plus aluminum addition, for example, causes trouble with surface films and reacts with oxygen and nitrogen, and hence makes the alloy difficult to cast in the absence of special techniques such as vacuum melting or controlled atmosphere. Columbium and molybdenum individually tend to lessen resistance to oxidation at 2000 F., and hence life expectancy is lessened. Tungsten, on the other hand, seems to have none of these drawbacks, and appears to enhance the strength of the austenite matrix aiforded by the nickel and chromium contents.

It is an object of the present invention to achieve hot strength characteristics in a heat and corrosion-resistant alloy of the nickel-base type but containing tungsten, and to do this by way of a limited cobalt addition, the preferred alloy of the present invention being further characterized by the absence of molybdenum, titanium and columbium.

Thus, in accordance with the present invention, it has been found that with tungsten present in a nickel base, heat-resistant alloy, life expectancy can be appreciably increased and minimum creep rate significantly lowered by adding cobalt. The data in Table I demonstrate the improvement, and here the variations in silicon, manganese, nickel, chromium and tungsten have no significant effect on hot strength data. Increasing carbon improves hot strength, and this is also true of optimum amounts of dissolved nitrogen. The balance for each alloy in Table I is substantially all iron, and this is also true of the other alloys disclosed herein in definite percentage amounts. The minimum creep rate is the minimum or so-called stage II creep rate of the standard constant temperature-constant load creep test.

TABLE I Properties of Cast Heat-Resistant Alloys a! 2000 F., 2500 p.s.z'. Stress 1 Minimum creep rate-percent/hr.

2 Zirconium, calcium and aluminum added as deoxidizers. Residual zirconium,f0l032%; residual aluminum 0.075%.

3 Deoxidized with aluminum only; residual, 0.077%.

4 Minimum values of 0.0003 and 0.0008 were obtained.

about 25 to 26 percent, and the present alloys are not cobalt base.

Heat and corrosion resistant alloys characterized by a nickel base and containing substantial amounts of chromium are known, and some include substantial amounts of Exceptional values of minimum creep rate (MCR in Table IIpercent per hour) were noted with the alloys in Table II at the indicated temperatures and under the indicated stress, and quite prolonged life (in hours) was obtained.

TABLE Ill.-HEAT RESISTANT ALLOYS Chemical Composition Properties 1800 F. and 8000 p.s.i. 2000 F. and 2500 psi. 2200 F. and 1000 p.s.i. Heat No.

Mn Si Or Ni 00 W N Life, MGR, Elong., Life, MGR, Elong, Life, MGR, Elong., hours peiifent percent hours pepcent/ percent hours pegocnt/ percent 2. ll. 1'.

Based on the data in Table II, and previous experiences from castings, since alloys of this kind are generally cast. with heat-resistant alloys, the following broad alloy However, forgings and other wrought products are posrange (any balance, substantially all iron) is compresible by appropriately lowering carbon, tungsten and cohended as one aspect of the present invention: balt.

Table HI sets forth limiting creep-rupture data per- I tinent to design calculations for the preferred alloy under 0% 51% Cr% 00% W% N% the present invention.

0.30 0.02 0.5 22 20 0 3 0.01 TABLE III 0. 05 1.25 2.0 32 42 20 10 0.15 Nominal Composition 0 Mn 81 Cr Ni 007 W N Fe For example, heats 11, 12 and 26, at the limits of the 35 l 0 carbon range (carbon enhances hot strength), display 010 I 28.0 l 36.0 I 15.0 I 5.0 laiol 14- excellent properties at 1800 F., 8000 p.s.1. which are rather severe conditions. The oxidation resistance of the alloy is excellent. However, the lowered carbon in a heats l1 and 12 needs to be compensated for by increasmess (PM) I01; ing tungsten and cobalt. To avoid the expense of exces- 40 1 sive tungsten and cobalt additions, while attaining desir- Temp" F Llfe (hours) MGR (percent/hm) able high temperature properties, the following range is inclusive of general purpose alloys contemplated herein: 100 1,000 (mm wool ,200 1 00 2, 08 I; 66 1, 7,000 0 00 1 0% Mn% 51% N1% 00% W% N% 1,000 5,100 3,300 3,300 2, 450 2, 3, 500 2, 250 2, 300 1, S30 2,100 2,250 1,300 1, 00 0 0.4 0.02 0.5 25 34 13 3.0 0.05 2 1,250 6 550 350 0.0 1.25 2.0 28 38 17 7.0 15 21300 500 5O In f h 1 The data in Table III are based on numerous creepf urt exp anatlon of the aboYe Preferred range rupture tests, some lasting for several thousand hours. f j; l t l m below For example, the 600 p.s.i. stress for 1000 hour life at f T P0581 oxldauor} resfstance' In 2200 F. is validated not only by log-log plotting of t i owarmost hmlt of 22% chmmmm the broad 55 various tests and by interpolation, but also by an actual .range 5 (mm not be alloys P are to b test at 2200 F. under 500 psi that endured 2868.1 JCCtGd to temperatures as high as 2260 F. In this same hours before fracture 1 .1 g i t t i of i m afidmml For hot gas corrosion resistance, good life at 1800 F. i 51 g g l 8 used cauflously requires that the surface metal loss be less than 0.1 1nch m par 5 W1 per year. At higher temperatures greater rates are R g? atmospneres W ere Catastlop oxldatlon 15 tolerated. As an example of surface stability, the above 51 & bd 1 h reep-rupture test at 2200" F. (Table III) showed a surth 0y l f. not i as a Smngt g undfir face metal loss of only 0.002 inch, which is equ1valent g l as g g g f i i to 0.006 inch per year. As with other heat reslstant a f n ac 2 1 S S avol g g y alloys there is some sub-surface attack below the layer i? a E i z' v t of protective scale that develops. This amounted to a 1 agcen ua es suscelplra 11 yh 0 6 021 as mp 10 X anon total of about 0.040 inch in 1869 hours at 2200 F. 01 9 1t1n ment1ne W ere 1t 15 f j Such 0.19 inch per year total metal affected. Only the upper ditions w1ll not be encountered, then 1t is possible to use quarter Of this depth was seriously ff t d hmlted amount of molybdenum 1f deslred for some Comparative tests under standardized thermal fatigue unique purpose. By the same token, the present alloy is also made without the need for additions of colurnbium, titanium or boron and like molybdenum, should be avoided in alloys for service at least as high as 2000 F.

The creep rupture data set forth herein were obtained conditions show that the alloy of Table III has unusually good resistance to this type of damage, using 15 minute temperature cycles of 300 to 1800 F. Comparison with industrial alloys usually selected for thermal fatigue service were favorable. Thus, one heat of the Table HI alloy lasted 180 cycles and another, 244 cycles before failure, while the known HW (12% Cr:60% Ni) grade gave 135 cycles and the popular HT (15% Cr:35% Ni) alloy en dured 158 and 202 cycles before failure.

The considerations establishing the ranges for some of the ingredients have been explained above. Silicon is essentially a deoxidizer. Nitrogen plus carbon content should not exceed 1.1% in order to avoid excess embrit tlement. Manganese should not be above the range indicated, in order to avoid excessive formation of spinel forming surface oxides which may impair oxidation resistance at very high temperatures. Calcium, zirconium, and aluminum can be used as special deoxidizers or degasifiers and these, with the usual contaminants, Will not analyze more than about 0.2%. The alloy heats under the present invention can be prepared in accordance with techniques conventional to the art, and the alloys require no special heat treatment. Structural parts can either be cast directly or forged as noted, and are readily machinable.

Heat resistant alloys are reported in British Patent Nos. 640,143 and 681,247. The highest temperature for service reported in the British patents appears to be 850 C., corresponding to 1562 F. It is important to realize that the alloy of the present invention displays excellent resis ance to oxidation at elevated temperatures above anything reported in the British patents. Thus, to first consider experimental heat X172, this analyzes as follows:

0% Mn% Si% Cr% Ni% N% Ob% This alloy has strength comparable to that of the British patents, namely, 20,000 p.s.i. at 1400 F. for 192 hours rupture time. Two related heats that differed from X172 significantly only in carbon variations (X190 and X1149: 0.64 and 0.66 carbon respectively) were exposed for over 3000 hours at 1900-1940 F. in an oxidizing atmosphere. Surface metal loss was 0.16-0.22 per inch per year and increasing. Similar excessive scaling rates were encountered with heats X6127 (0.31 carbon) and X6128 (0.36 carbon). In these four instances, the nickel is in the mid-range of British Patent No. 640,143 and quite close to the examples cited in British Patent No. 681,247, but the material is undesirable for service at 1900-1940 F. Additionally, solution heat treatment followed by aging is specified, but the present alloys have the properties specified in the as cast state. The following table sets forth the oxidation resistance of the present alloy at 2200 F.:

TABLE IV Surface Dimension Heat N0 Temp., F. Time, hours Change, inches per year NOTE: values indicate an increased dimension because of a thin protective scale build-up.

212992 reported in aforesaid iron and Steel Engineer had a duration at 2500 p.s.i. stress of 289 hours and a minimum creep rate of 0.012. The allow of heat No. 5 reported in aforesaid Iron and Steel Engineer under the same conditions had a life of 139 hours and a creep rate of 0.041. The fundamental differences between the Iron and Steel Engineer heat No. 212992 and heat No. 5 were lower nickel for the alloy of heat No. 5 (48.9 vs. 43.1), slightly higher chromium (26.1 vs. 27.8) and about the same tungsten (6.16 vs. 5.92).

The following table contrasts the performance of three additional alloys, reported in aforesaid Iron and Steel Engineer, with an alloy of the present invention at 2300 F.

TABLE V COMPOSITION Heat No 0 Mn Si Ni Cr W (S e Table II above 0.44 0.80 1. 03 49. 3 29.0 4. 96 0. 57 1.21 1.00 48.6 26.2 4 96 0. 60 1.43 1. 46 46. 8 26. 4 5.14

CREEP AND STRESS RUPTURE DATA Heat No. Temp, Stress, Rupture MGR,

F. p.s.i. time (hrs.) percent/hr.

1 Reported at Iron and Steel Engineer, February 1953, page 105.

It will be seen from the foregoing that under the present invention hot strength characteristics have been greatly improved in respect of a heat and corrosionresistant alloy of the nickel-chromium type containing tungsten, and this has been accomplished by adding cobalt. The present alloy is to be distinguished from a cobalt base alloy, and is further distinguished by the absence of molybdenum, columbium and titanium. Iron is not essential as will be evident from heat No. 22 in Table 11. Hence, while preferred examples of the invention have been described, these are capable of some variation and modification.

I claim:

1. A heat and corrosion resistant alloy consisting es sentially of: carbon, 0.3-0.95%; silicon, 0.5-2%; nickel, 26-42%; chromium, 22-32%; tungsten, 3-16%; cobalt, 9-26%; balance, if any, essentially iron.

2. A heat and corrosion resistant alloy for service at temperatures at least as high as 2000 F. and, for this purpose, consisting essentially of: carbon, about 0.4- 06%; silicon, about 0.5-2%; nickel, about 34-38%; chromium, about 25-28%; tungsten, about 3-7%; cobalt, about 13-17%; nitrogen, about ODS-0.15%; balance, essentially iron.

3. A heat and corrosion resistant alloy for service at high temperatures and for this purpose, consisting essentially of carbon, about 0.4-0.6% silicon, about 0.5-2%; nickel, about 34-38%; chromium, about 25-28%; mgsten, about 3-7%; and cobalt, about 13-17%; balance, essentially iron. 

1. A HEAT AND CORROSION RESISTANT ALLOY CONSISTING ESSENTIALLY OF: CARBON, 0.3-0.95%; SILICON, 0.5-2%; NICKEL, 26-42%; CHROMIUM, 22/32%; TUNGSTEN, 3-16%; COBALT, 9-26%; BALANCE IF ANY, ESSENTIALLY IRON. 